The rombohedron is muce similar to a twisted cube.

 

you can  easely make a cube cristal from home salt :

 

1. Boil a pot of hot water and pour in a jar.

 

2. Add about 2-3 tablespoons of salt to the mixture and stir with a spoon until you can't see the salt grains.

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3. Keep adding salt until the salt no longer dissolves.

 

4. Put on the lid, then shake the jar.

 

5. Tie a string around a pencil or small stick.

 

6. Cut the string so that it hangs into the water.

 

7. Balance the pencil on top of the glass jar with the string hanging inside the jar, extending into the water.

 

8. Leave it in a sunny place for at least two days, then check back every day to see if there are salt crystals on the string.

 

for video instruction go to - 

http://www.marthastewart.com/1004005/how-make-monster-salt-crystals